Not sure. But the idea that I didn’t have bugs in late iOS 18.7 is so absurd. Late iOS 18 wasn’t bug free or stable. I remember all the calls for senior advisors and engineering reporting bugs. Even going as far as fresh iOS install at an Apple Store to rid of them (some fixed. some didn’t).Did the bug you reported exist in iOS 18?
Apple removed security fixes made available in a 18.7.3 build from the public. Users do want ensure we have the latest security and bug fixes.
Apple thinks 'different'.
I reckon Apple simply doesn’t want to do every iOS prior I would guess.